A data transmission method and device, where the method includes determining, by a first station device, that a second station device supports a first service, receiving a device group join request message that is sent by the second station device according to a media access control (MAC) address of a first device group, where the first device group is a device group of the first service and is a device group to which the first station device belongs, sending a device group join response message to another station device in the first device group and the second station device according to the multicast MAC address of the first device group in a contention transmission manner, and performing data transmission of the first service with the second station device in a service window of the first service, where the service window includes a time and/or a channel of service transmission.